Recent advances in the HIV vaccine research field have led to renewed optimism that vaccine-elicited antibody responses can contribute to protection against HIV-1 infection. These advances include the discovery of more than 40 antibodies with broad neutralization activity against genetically diverse HIV-1 strains, and the correlation of antibody responses with protection in the RV144 phase III vaccine trial. In preclinical studies in nonhuman primates (NHP), using SIV immunogens and challenge virus, we have demonstrated that inclusion of an immunostimulatory ligand, CD40L, and deletion of immunomodulatory genes from the MVA vaccine vector, both augment vaccine-elicited antibody responses. In the case of . CD40L, antibody avidity, neutralizing activity, and specificity were enhanced and correlated with protection against acquisition. Here in Project 3 we will investigate the effects of CD40L on antibody responses elicited against clade C HIV-1 immunogens in NHP in Project 2, and in human subjects enrolled in a phase I clinical trial in Project 1. Furthermore, we will look for potential synergy between CD40L and the modified MVA vaccine vector when used in combination. Project 3 will specifically characterize the antibody responses elicited by these immunization regimens, and compare responses in NHP and humans that received analagous vaccines. The hypotheses to be tested in Project 3 are (i) that inclusion of the CD40L adjuvant will focus the vaccine-elicited antibody response on potentially protective epitopes, (ii) this focused response will be associated with enhanced protection against challenge in NHP, (iii) the MVAA4 will further augment the protective antibody response elicited by the CD40L adjuvanted vaccine by increasing the magnitude of the response, and (iv) similar antibody profiles will be observed in humans and NHP that received analogous CD40L adjuvanted vaccines. The use of an innovative and broad set of experimental tools, combined with the comparison of antibody responses and specificities elicited in human subjects and NHP, will inform us about important similarities and differences that bridge the translational gap between pre-clinical and Clinical vaccine studies.